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Abstract

Studies of patients and animals with brain lesions have implicated the hippocampal formation in
spatial, declarative/relational and episodic types of memory. These and other types of memory consist
of a series of interdependent but potentially dissociable memory processes—encoding, storage,
consolidation and retrieval. To identify whether hippocampal activity contributes to these processes
independently, we used a novel method of inactivating synaptic transmission using a water-soluble
antagonist of AMPA/kainate glutamate receptors. Once calibrated using electrophysiological and
two-deoxyglucose techniques in vivo, drug or vehicle was infused chronically or acutely into the dorsal
hippocampus of rats at appropriate times during or after training in a water maze. Our findings
indicate that hippocampal neural activity is necessary for both encoding and retrieval of spatial
memory and for either trace consolidation or long-term storage.